PUMP ARRANGEMENT FOR AN OIL BURNER AND METHOD FOR REGULATING THE CAPACITY OF THIS OIL BURNER

Abstract: A pump arrangement (1) for an oil burner has a connection (6) at which oil is delivered at a constant pressure, and a device for creating a modulated pressure, in particular a modulation valve (18). A change-over device (21) applies the constant or the modulated pressure selectively to the connection (6). A method for regulating the capacity of an oil burner operates with a first power level, which may be switched on and off and which delivers oil at a constant pressure to the atomizer unit (2), and with a reduced second power level in which oil is delivered at modulated pressure. In this manner, power regulation can be effected without the oil burner having to be switched off.

Description: Pump arrangement for an oil burner and method for regulating the capacity of this oil burner. The invention relates to a pump arrangement for an oil burner according to the preamble of claim 1, and to a method for regulating the capacity of an oil burner according to the preamble of claim 14. Known oil burners, as commercially available for heating purposes, operate with a predetermined power level at which the pump arrangement delivers the oil at a constant, generally adjustable, pressure to the atomizer unit, in particular a nozzle. Matching the pump output to the required heat output of the boiler or similar vessel is effected by switching the oil burner on and off. Incomplete combustion resulting from this switching on and off pollutes the environment, however, and causes deposits to form on the nozzle and in the combustion chamber and so on. From DE 41 13 067 Al it is known to supply the oil in pulses to the atomizer unit and to adjust the desired output by influencing the pulses, for example, by the pulse frequency. For that purpose, the pressure-side output of the continuously operating supply pump is connected by way of a non-return valve, which opens only when the oil pressure is above 2 bars, to the atomizer unit and is connected by way of a rhythmically controllable electromagnetic valve to the oil reservoir. When the electromagnetic valve is closed, a pressure builds up at the pressure-side output of the pump which leads to the non-return valve opening and which can be, for example, 10 bars. If the electromagnetic valve opens, this pressure collapses, the non-return valve closes and atomization is interrupted. At a pulse frequency of 3 Hz and a pulse duration of 0.03 sec, the oil throughput can be reduced to about 20% of the amount that is delivered with a permanently closed electromagnetic valve. The service life of the electromagnetic valve is limited, however, because of the high frequency with which it opens and closes. In addition, there is a high noise level. It is the aim of the invention to specify new ways of matching the amount of oil that is supplied to the atomizer unit of an oil burner to requirements. This aim is achieved in practically by the features of claim 1. The pump arrangement has two operational states, in which, with the pump running, different amounts of oil are delivered. Demand can be matched by use of a conventional thermostat which, by operating the change-over device, alternately causes the first or the second operational state to be effective at the connection leading to the atomizer unit. Since the intervals during oil feed with modulated pressure are so brief that the flame in the combustion chamber is not extinguished, a continuous operation with proper power regulation can be achieved, without the disadvantages mentioned in the introduction as a result of the pump switching on and off occurring. In the construction according to claim 2, the change-over device is constituted by the on-off valve which, on account of its low operating frequency, has a long service life even when in the form of an electromagnetic valve. The modulation valve requires no special regulation, since the change-over device already exists for that purpose. The modulation valve can therefore be of simple construction, operate at a constant switching rate, and for example, be mechanically driven. In preferred embodiment according to claim 3, two outputs are provided with constant or modulated pressure. The mode of operation of the second output can be achieved most simply with a modulation valve which connects the second output alternately with the output side and the intake or return side of the pump. Here too, the modulation valve does not need to be regulated. It is sufficient for modulation to be effected at a constant frequency and pulse shape. A very simple solution is obtained according to claim 4, which provides a rotary pump with rotary slide valve which takes on the function of the modulation valve. The gear pump according to claim 5 is particularly advantageous for the construction of the rotary slide valve. It is also an advantage that such a gear pump as a heating oil pump has proved a millionfold success. The embodiments of claims 6 to 9 show that conventional pumps can be provided with a modulation valve with very little modification, and therefore correspondingly cheaply. By means of a pressure regulating valve according to claim 10, the pressure at the first output can be kept strictly constant. Using a second output, which is temporarily connected to the output side and therefore to the first output, the maximum amplitude of the modulated pressure is also limited to the set value. In the development according to claim 11, the pump arrangement can be operated at two different pressure levels. The normally operative higher-pressure regulating valve loses its function when the second lower-pressure regulating valve is rendered operative by the on-off valve. In this manner, four power levels are achieved, because the two pressure levels have an influence on the conditions both at the first output and at the second output. By controlling the said on-off valve and the change-over device, power can therefore be influenced over a large operating range. If the change-over device according to claim 12 consists of two on-off valves, no additional on-off valve is required to disconnect completely the line leading to the atomizer unit. The non-return valve according to claim 13 ensures in a manner known per se that the atomizer unit is supplied with oil only when the oil has reached a sufficiently high atomization pressure. The problem of the invention is solved by the method having features specified in claim 14. By using two power levels, power matching in the context of on-off control is possible, without the oil feed having to be switched off. The development according to claim 15 has the advantage that the pressure preset for the first power level is also effective for the second power level. The construction according to claim 16 leads to a total of four power levels with which the capacity control can be effected over a very large power range. The invention is explained in detail hereinafter with reference to preferred embodiments illustrated in the drawings, in which Fig. 1 shows diagrammatically the circuit diagram of a pump arrangement according to the invention, Fig. 2 shows a second embodiment of a pump arrangement according to the invention, Fig. 3 is a graph of pressure plotted against time, Fig. 4 is a longitudinal section through a gear pump with a built-in modulation valve, Fig. 5 is a plan view of the gear pump of Fig. 4, assuming the cover plate to be transparent, Fig. 6 shows a modified embodiment in a view similar to that of Fig. 4, Fig. 7 is a plan view of the embodiment of Fig. 6, assuming the cover plate to be transparent, Fig. 8 shows a further embodiment of the pump arrangement and Fig. 9 shows a section through the drive shaft of that embodiment. Fig. 1 shows a pump arrangement 1 for an oil burner having, in addition to a blower, not illustrated, an atomizer unit 2 with an atomizing nozzle 3, and a non-return valve 4, which opens only when an adequate atomization pressure is present. An associated nozzle line 5 is connected to a connection 6 of the pump arrangement 1. The pump arrangement has a rotary pump 7 which draws oil from a reservoir 8 by way of an intake line 9 and a filter 10 and then feeds it from the intake side 11 to the output side 12. This output side 12 is connected by way of a throttle 13 to a return line 14 leading to the reservoir 8. Parallel therewith there is arranged a pressure-regulating valve 15, which keeps the pressure of the output side 12 constant at an adjustable value. Between the intake side 11 and the return line 14 there is moreover a non-return valve 16 which becomes effective whenever the system operates in single-line mode. The output side 12 forms a first output 17. A modulation valve 18, the rotary slide valve of which is rotated by the shaft 19 of the rotary pump 7, connects a second output 20 alternately to the output side 12 and the intake side 11 of the rotary pump 7. At the first output 17 there is therefore a constant oil pressure available, and at the second output 20 a modulated oil pressure. A change-over device 21 consists of a first on-off valve 22 and a second on-off valve 23, both of which are in the form of electromagnetic valves. The first on-off valve 22 is arranged between the first output 17 and the connection 6, the second on-off valve 23 is arranged between the second output 20 and the connection 6. When the on-off valve 22 is open, the oil burner is therefore supplied with a first power level, and when the on-off valve 23 is open, the oil burner is supplied with a second power level of reduced heating capacity. A temperature sensor 24 relays the boiler temperature, that is, the temperature of the water warmed by the heated boiler, to a regulator 25, which is preset at a desired temperature 26. The regulator controls the on-off valves 22 and 23 by way of the signal lines 27 and 28. When the temperature is too low, the first output 17 becomes effective, and at too high a temperature the second output 20 becomes effective. The individual pulses of modulated pressure follow each other so quickly that the flame in the combustion chamber is not extinguished but ignites the freshly supplied oil immediately. In this manner the burner can be operated as it were continuously, so that the problems (environmental pollution and the like) associated with switching the system on and off are avoided. In the embodiment of Fig. 2, the same reference numerals as in Fig. 1 are used for corresponding parts. A new feature is that the modulation valve is built into the rotary pump 29. Furthermore, in a branch parallel to the first pressure regulator 15, a second pressure regulator 30, which is set to a lower pressure than the first pressure regulator 15, is arranged in series with an on-off valve 31. The latter is illustrated as a normally open electromagnetic valve and is operated by way of a signal line 32 by the regulator 25. If the on-off valve 31 is closed, there is a higher pressure on the output side 12, but if the on-off valve 31 is open, there is a lower pressure. With the on-off valve 31 closed, the operating conditions are the same as in Fig. 1. With the on-off valve 31 open, conditions are similar but at a lower pressure or power level. Fig. 3 illustrates four power levels A, B, C and D, the power levels A and B applying to both embodiments. The largest feed rate, and thus the greatest power, is obtained at power level A, at which the feed pressure PI is constant. In that case the on-off valve 22 is open, while the on-off valves 23 and 31 are closed. A lower power is achieved at stage B, when a modulated pressure with a maximum amplitude PI is present. In that case the on-off valve 23 is open, while the on-off valves 22 and 31 are closed. Next is power level C, where the lower pressure P2 is maintained constant. This happens when the on-off valves 22 and 31 are open and the on-off valve 23 is closed. Last is power level D, which provides a modulated pressure with a maximum amplitude P2. For that purpose the on-off valves 23 and 31 must be open, while the on-off valve 22 is closed. It is obvious that the regulator 25, which controls all three on-off valves 23, 23, 31, allows power to be modified over a very wide range. Figs 4 and 5 show a gear pump with a built-in modulation valve. A housing 33 has a cylindrical recess 34 which is covered over by a cover plate 35 and receives a rotatable gear ring 36 with internal teeth. The gear ring forms pockets 37 with an externally toothed gearwheel 38 which is arranged eccentrically with respect to the gear ring 36 and is driven by way of a shaft 39 by a motor. In the cover plate 35 there is a pressure groove 40, which is connected by way of a channel 41 to the output side 12, and an intake groove 42, which is connected by way of a channel 43 to the intake side 11. Such a pump is known as a gerotor gear pump. On the outer circumference of the gear ring 36 there is an annular groove 44. Leading from that is a radial channel which forms a valve opening 45. During rotation of the gear ring 36, the valve opening communicates alternately with the region below the pressure groove 40 and with the region below the intake groove 42. In addition, the annular groove 44 is connected to a channel 46 which leads to the second output 20. This second output is consequently alternately pressurized with high pressure and with intake or return pressure, that is, with modulated pressure. In the embodiment of Fig. 6 and 7, the gear pump is of the same construction as in Figs 4 and 5. Reference numbers increased by 100 have therefore been used for corresponding parts. The essential difference is that in the cover plate 135 there is formed an annular groove 144 which extends along the front face of the gear wheel 138 and is connected to a line 146 leading to the second output 20. A recess in the front face of the gear wheel 138 serves as the valve opening 145. This recess extends radially into the region of the pressure groove 140 and the intake groove 142. On rotation of the gear wheel 138, this valve opening 145 communicates alternately with the output side and the intake side. Here too, a modulated pressure consequently forms at the second output 20. In the embodiment according to Figs 8 and 9, in which reference numbers increased by 200 have been used for corresponding parts, the drive shaft 239 of the rotary pump 7, which has a valve opening 245 in the form of part of an annular groove, forms the modulation valve 218. In the associated housing 233 there is a valve opening 240 in the form of a bore which is connected to the output side 12 of the pump, and a valve opening 242 in the form of a bore which is connected to the intake side 11 of the pump. The modulation valve 218 is in series with an on-off valve 221 arranged between the output side and the return line 14 and serving as the change-over device. If the on-off valve 221 is opened, there is modulated pressure present at the connection 6, if it is closed, there is a constant pressure.

Claims: Patent Claims 1. A pump arrangement for an oil burner, which delivers oil at a constant pressure at a connection for a line leading to an atomizer unit, characterized by a device for creating a modulated pressure and by a change-over device (21) which applies the constant or the modulated pressure selectively to the connection (6). 2. A pump arrangement according to claim 1, characterized in that the output side (12) of a pump (7) arranged to be connected to the connection (6) is connected by way of the series connection of an on-off valve (221) and an alternately opening and closing modulation valve (218) to the intake or return side (11) of the pump. 3. A pump arrangement according to claim 1, characterized in that the output side (12) of the pump (7, 29) arranged to be connected to the connection (6) forms a first output (17) , a modulation valve (18) connects a second output (20) alternately to the output side (12) and the intake or return side (11) of the pump, and the change-over device (21) connects the first or the second output (17, 20) selectively to the connection (6) . 4. A pump arrangement according to one of claims 1 to 3, characterized in that a rotary pump (7, 29) is provided, and the modulation valve (18; 218) comprises a rotary slide valve which is connected to a rotating part of the pump. 5. A pump arrangement according to one of claims 1 to 4, characterized in that the rotary pump (7, 29) is a gear pump with a rotating inner gear wheel (38; 138) and, meshing therewith, an outer gear ring (36; 136) mounted eccentrically with respect to the gear wheel. 6. A pump arrangement according to claims 3 to 5, characterized in that associated with the rotary slide valve there is an annular groove (44; 144) which is connected on the one hand to a valve opening (45; 145) , which valve opening is moved in succession past output side and intake side, and on the other hand to the second output (20) . 7. A pump arrangement according to claim 6, characterized in that the annular groove (44) runs along the circumference of the gear ring (36) and the valve opening (45) is formed by a radial channel in the gear ring. 8. A pump arrangement according to claim 6, characterized in that the annular groove (144) runs radially within the pressure groove (140) and intake groove (142) of the rotary pump along the front face of the gear wheel (138) and the valve opening (145) is formed by a recess in the front face passing over the pressure groove and intake groove. 9. A pump arrangement according to claim 2 and 4, characterized in that the drive shaft (239) of the rotary pump has an annular groove portion (245) which during a part of the rotation connects together two valve openings (240, 242) arranged in the enclosing housing (233) , of which one valve opening is connected to the output side (12) and the other valve opening is connected to the intake or return side. 10. A pump arrangement according to one of claims 1 to 9, characterized in that the output side of the pump (7, 29) is connected by way of a pressure-regulating valve (15) to the return side. 11. A pump arrangement according to claim 10, characterized in that parallel with the first higher- pressure regulating valve (15) there is arranged the series connection of a second lower-pressure regulating valve (30) and an on-off valve (31) . 12. A pump arrangement according to one of claims 3 to 11, characterized in that the change-over device (21) consists of two on-off valves (22, 23) which are arranged in the line between the first (17) and second output (20) respectively and the connection (6) . 13. A pump arrangement according to one of claims 1 to 12, characterized in that a non-return valve (4) which opens as soon as a preset atomization pressure is exceeded in arranged in the atomizer unit (2) . 14. A method for regulating the capacity of an oil burner by means of a pump arrangement, in particular a pump arrangement constructed according to one of claims 1 to 13, which delivers oil at a constant pressure to the atomization unit in a first power level which can be switched on and off, characterized in that in addition to being operable with the first power level, the pump arrangement is also operable at least with a reduced second power level in which oil is delivered at modulated pressure, and the regulation is effected, with the pump running constantly, by selective operation with the first or another power level. 15. A method according to claim 14, characterized in that the modulated pressure fluctuates between the pressure of the first power level and the intake or return pressure. 16. A method according to claim 14 or 15, characterized in that the pump arrangement is also operable with a third power level in which oil is supplied at a constant pressure that is lower than with the first power level, and with a fourth power level in which oil is supplied at a modulated pressure, the maximum amplitude of which is smaller than with the second power level.

Inventors: KIRKELUND POUL, KIRKELUND, POUL
Applicants: DANFOSS AS, KIRKELUND POUL, DANFOSS A/S, KIRKELUND, POUL
Application year: 1994
Main classification: F23K5
IPC codes: F04B49, F04C14, F23K5